Process of forming cellulosic webs containing urea-alkyleneimine condensation products



In the manufacture of 'cellulosic fibrous materials, in particularpapers, cardboards and cellulosic pulps, it is usual to employ auxiliaryagents besides the fibrous material or paper material. Such auxiliaryagents are intended, for example, to shorten the time necessary todewater the paper pulp or to increase the tensile strength of thefinished product in the wet or dry state, or to modify, for example, thewater absorbability, the surface smoothness or other properties.Auxiliary agents are also used which are capable of retaining to a largeextent or of depositing other products on the fibrous material, forexample, pigments. Thus, for example, for increasing the speed ofdewatering of a pulp of fibrous material, surface-active substances ofthe alkylaryl-sulfonate type have been used. The wet tensile strength orthe wet scufiing resistance can be increased, for example, by productsthat are based on melamine-formaldehyde precondensates or similarcompounds; these products may be applied alone or, if required, togetherwith other products such as plasticizing, filling or pigmentingadditives. For retaining the fibrous material or the filling materialduring the formation of the paper web, there are used, for example, boneglues or similar substances and water-soluble highly polymericsubstances based, for example, on polyacrylamide. I

Now, we have found that in the manufacture of cellulosic fibrousmaterials, in particular paper, cardboard and cellulosic pulps, some ofthe afore-mentioned effects can be produced simultaneously by adding tothe aqueous suspension of the fibrous material, prior to the formation'of a paper web, water-soluble or in water self-emulsifying,nitrogen-containing condensation products of 1,2- alkyleneimines inwhich one of the hydrogen atoms at the nitrogen is substituted, and/ ortheir oligomers with urea.

For-preparing the water-soluble or in water self-emul- United StatesPatent-O carried out in the molten mass, i.e. in the absence of solventsor diluents. This method of operation permits, for example, theconversion of the oligomeric ethyleneimines or 1,2-propyleneimines withurea into resinous condensation products. When following this method ofoperation, there is first obtained a highly viscous, amorphous masswhich is still soluble in water. Upon further heating, there are formedcross-linked products which are only swellable in water. Preferably,however, the reaction of the 1,2-alkyleneimines with urea is carried outin a solvent or diluent or in a mixture of such substances, in order towithdraw easier the reaction heat. As solvents or diluents, there aresuitable all products which do not react with the alkylene-imines. Assuch, there may be mentioned alcohols, esters, amides, and evenhydrocarbons. The use of water as the diluent is especiallyfavorsifying, nitrogen-containing condensation products of 1,2-

alkyleneimines and urea, there may be used 1,2-a1kyleneimines which arenot substituted at the nitrogen atom. Preferably, there are used easilyaccessible imines having small alkylene radicals, for example,ethyleneimine, 1,2-propyleneimine, 1,2- or 2,3-butyleneimine or2,2-dimethylethyleneimine. Instead of the monomeric cyclic compounds,there may also be used the dimeric, trimeric and other oligomeric forms,especially, however, the oligomers of ethyleneimine and of1,2-propyleneimine. The preparation of the oligomeric alkyleneimines isdescribed in the hand book by Houben-Weyl, Methoden der organischenChemie, 4th edition, volume XI/2,

page 261, 1958.

For preparing the condensation products, it is not necessary to use thepure oligomeric 1,2-alkyleneimines for the reaction with urea. Theoligomeric mixture as it is obtained in the preparation of thealkyleneimines may also be reacted with urea, if required or desired, inthe presence of the monomeric alkyleneimine. The reaction yielding thecondensation products proceeds exothermically with separation ofammonia. The reaction can be able and advantageous from a technicalpoint of View. The quantity of the water used can vary within widelimits. Even when the reaction is carried out in a diluent, for example,water, there are first formed low molecular,

'still soluble products, which can then be converted into insolublecross-linked products by further heating.

The reaction of the components is carried out at elevated temperature,namely in a temperature range of from about 40 C. to about 200 0.,preferably from about 60 C. to about 140 C. If water is used, thereaction is suitably carried out at about C. and the aqueous reactionmixture is then kept boiling weakly. The preparation of the condensationproducts is usually carried out at normal pressure. For removing the am-I monia which is forming during the reaction, it may be of advantage toapply a reduced pressure. On the other hand, the reaction time isshortened, if, especially in the case of a reaction in aqueous solution,the reaction mixture is allowed to boil at elevated temperature, forexample, in a range of from 100 C. to C., by the application ofoverpressure. The condensation products obtained are highly viscous tosolid amorphous masses of high molecular weight.

The products may also be obtained in non cross-linked form and are inthis state water-soluble. When the reaction is continued untilcross-linking of the reaction product is achieved, glass-like orgelatin-like solidified masses are obtained which are only swellable inwater.

As the condensation products which may be used according to the presentinvention, those products are especially considered in which the ratioof urea to alkyleneimine is in the range of 0.25 to 1.5 mol of urea,preferably 0.5 to 1.3 mol of urea, per 1 mol of alkyleneimine. Molecularproportions of somewhat more than 1 mol of urea per 1 mol ofalkyleneirnine are of special interest. Instead of alkyleneimines, theremay also be used in the same quantitative proportions their oligomers.If the alkyleneimines are mixed with oligomer s, they may be mixed inany desired quantitative proportion.

The nitrogen-containing condensation product of 1,2- 'alkyleneimines andurea-to be added according to the present invention to the aqueoussuspension of the fibrous material-are usually added in quantities ofabout 0.1 to about 4%, preferably 0.2-l%, referred to the dry fibrousmaterial. The condensation products may be added either during thebeating of the fiber material or shortly before it is transferred on thewire. Other products, for example, plasticizing, glueing or antistaticagents may then also be added to the usual extent. It is also possibleto apply with the products to be used according to the presentinventionabout 1.5-8%, preferably 24%, referred to the dry fibermaterial, of condensation products of urea and formaldehyde and/ ortriazines and formaldehyde. In the case of mixtures of urea/formaldehydecondensation products with such of triazines and formaldehyde, themolecular proportion may have any desired ratio. In certain cases, afurther increase of the wet strength and wet scufiing resistance canthereby be achieved. The fibrous material is then further treated andfinished in known manner; it does not'turn yellow atthe dryingtemperatures usually applied.

The application of the condensation products of 1,2-alkyleneimines andurea distinctly shortens the time necessary for dewatering the paperweb. In addition thereto, the wet tensile strength is considerablyincreased, a special advantage being that the absorbency of a fibrousmaterial thus prepared is practically not reduced. This advantagerenders the process especially suitable for the manufacture of filterpapers.

The use of the condensation products according to the present inventionalso brings about an increased retention of the fiber and fillingmaterials. As compared with the polyethyleneimines proposed for asimilar use, the compounds to be used according to the present inventionare distinguished by an essentially lower tendency to yellowing of thepapers prepared therewith, in particular at elevated temperatures.

The following examples illustrate the invention, but they are notintended to limit it thereto:

Example 1 A condensation product of 1 mol of ethyleneimine and 1.1 molof urea was added during beating in concentrations of 0.5%, 1%, 2%, and3%, referred to absolutely dry substances, to different cellulosic pulpsuspensions, and a paper sheet was formed from each of these suspensionson a sheet form. For comparison, a paper sheet having the same weightwas prepared from the same cellulosic pulp suspensions, but withoutaddition of auxiliary agents. The physical determination of the wettensile strength and of the water absorption by measurement of thesuction height gave the following results:

The above table shows that the wet tensile strength was distinctlyincreased, while the water absorption was not reduced.

Example 2 A condensation product of 1.5 mol of urea and 1 mol ofethyleneimine was added in a quantity of 0.4 and 1%, referred toabsolutely dry material, to a cellulosic pulp suspension having abeating degree of 75 S-R and a pH-value of 4.7 in a paper mill beater.In another experiment, the pH-value of the suspension was adjusted to7.5. The effect of the reduction of swelling and of the increase of thespeed of dewatering could be determined in known manner by measuring thereduction of the beating degree according to SR and the time requiredfor dewatering The following values were determined:

The above Values show that the speed of dewatering was distinctlyincreased in the neutral as well as in the alkaline pH-range.

Example 3 To a cellulosic pulp suspension having a beating degree of 455-H. and containing as a filler 40% of kaolin, referred to absolutelydry material, there were added 2%, referred to absolutely dry material,of a condensation product of 1 mol of urea and 2 mols of ethyleneimine.For determining the filler retention effect, the weights per squaremeter and the ash content of the papers finished with or withoutaddition of the condensation product as well as the content of solidsand floating particles in the waste water was measured after adjustmentof the equilibrium in the wire water circulation.

The following values were obtained:

Without 2% addition addition G/m. 68 70. 2 Ash content, percent 16. 718. 1 Content in waste water, mg 340 174 Example 4 Paper sheets wereformed from the following mixtures with bleached sulfite pulp having abeating degree of 40 S-R:

Sheet No.

Pulp (bleached sulfite 40 g T102, g- BaSO g Kaolin, g Product A, percentabs. dry

subst., g A. Product B, perze it abs. dry

subst., g

obtained showed a distinct increase of the retention by the addition ofthe condensation product of alkyleneimine and urea according to theinvention, in comparison with that of the paper prepared without thisaddition as shown by comparison of test 4 with 3 and test 6 with 5.

Sheet No. Mean ash value, g. Residue in g./l. of wire waste water Weclaim:

1. The process for preparing cellulosic fibrous materials havingincreased wet tensile strength, wherein to the fibrous material inaqueous suspension is added 0.1 to 4% on basis of the dry fibrousmaterial a nitrogen-containing condensation product of 0.25 to 1.5 moleto 1 mole, respectively, of urea and a member selected from the groupconsisting of 1,2-alkyleneimines, oligomers of 1,2-alkyleneimines, andmixtures of 1,2-alkyleneimines and their oligomers, and thereafterdewatering said suspension, sheeting the fibrous material and drying thesheeted material.

2. The process for preparing cellulosic fibrous mate rials havingincreased wet tensile strength, wherein to the fibrous material slurryis added on basis of the dry fibrous material 0.1 to 4% a Water-soluble,nitrogen-containing condensation product of 0.25 to 1.5 mole to 1 mole,respectively, of urea and a member selected from the group consisting of1,2-alkyleneimines, oligomers of 1,2-alkyleneimines, and mixtures of1,2-alkyleneimines and their oligomers wherein said nitrogen-containingmaterial is on basis of an absolutely dry material, and dewatering saidfibrous material slurry, sheeting the fibrous material and drying thesheeted material. 3. The process for preparing cellulosic fibrousmaterials having increased wet tensile strength, wherein to the fibrousmaterial slurry is added 0.1 to 4% on basis of the dry fibrous materiala nitrogen-containing condensation product of 0.25 to 1.5 moles to 1mole, respectively, of urea and a member selected from the groupconsisting of 1,2-alkyleneimines, oligomers of 1,2-alky1eneimines, andmixtures of 1,2-alkyleneirnines and their oligomers, and, additionallyadding to said slurry 1.5 to 8%, on basis of the dry fibrous material,condensation product selected from the group consisting of urea withformaldehyde, triazines with formaldehydes, and mixtures thereof, andthereafter dewatering said fibrous material slurry, sheeting the fibrousmaterial and drying the sheeted material.

4. The process for preparing cellulosic fibrous materials havingincreased wet tensile strength, wherein to an aqueous suspension of thefibrous material is added on basis of dry fibrous material 0.1 to 4%, ofwater-soluble, nitrogen-containing condensation products of 0.25 to 1.5moles to 1 mole, respectively, of urea and a member selected from thegroup consisting of 1,2-alkyleneimines, oligomers of 1,2-alkyleneimines,and mixtures of 1,2- alkyleneimines and their oligomers wherein saidnitrogencontaining material is on the basis of an absolutely drymaterial, and, additionally adding to the aqueous suspension of fibrousmaterial, 1.5 to 8% a condensation product selected from the groupconsisting of urea with formaldehyde, triazines with formaldehyde, andmixtures of condensation products of urea/formaldehyde andtriazine/formaldehyde wherein said formaldehyde condensation product ison basis of absolute dry material, and thereafter dewatering saidaqueous suspension of fibrous material, sheeting the fibrous materialand drying the sheeted material.

References Cited UNITED STATES PATENTS 467,655 12/1951 Italy.

S. LEON BASHORE, Primary Examiner.

1. THE PROCESS FOR PREPARING CELLULOSIC FIBROUS MATERIALS HAVINGINCREASED WET TENSILE STRENGTH, WHEREIN TO THE FIBROUS MATERIAL INAQUEOUS SUSPENSION IS ADDED 0.1 TO 4% ON BASIS OF THE DRY FIBROUSMATERIAL A NITROGEN-CONTAINING CONDENSATION PRODUCT OF 0.25 TO 1.5 MOLETO 1 MOLE, RESPECTIVELY, OF UREA AND A MEMBER SELECTED FROM THE GROUPCONSISTING OF 1,2-ALKYLENEIMINES, OLIGOMERS OF 1,2-ALKYLENEIMINES, ANDMIXTURES OF 1,2-ALKYLENEIMINES AND THEIR OLIGOMERS, AND THEREAFTERDEWATERING SAID SUSPENSION, SHEETING THE FIBROUS MATERIAL AND DRYING THESHEETED MATERIAL.